FIG. 1 shows a conventional shielding device 10, which is soldered to a printed circuit (PC) board 15 to prevent the electromagnetic wave generated by the electronic circuits on the PC board 15 from interfering with communication and human health. The shielding device 10 includes a rectangular upper lid 11 and a rectangular frame 12. The frame 12 has four side walls 13. Since any two adjacent side walls 13 are connected to each other only via a snap-fitting structure, there is a gap 14 left at every joint of two adjacent side walls 13. Total four gaps 14 are formed on the shielding device 10 to very possibly form paths via which electromagnetic wave enters into or leaks out of the shielding device 10. Leakage of electromagnetic wave is resulted from the unshielded gaps 14 and will interfere with communication and human health. Therefore, it is necessary to work out a way to shield the unshielded gaps 14 on the shielding device 10.